do_mounts.c: Minor ROOT_DEV comment cleanup

The ROOT_DEV comment is no longer accurate, it now seems to be
initialized in init/do_mounts.c.
Signed-off-by: Florin Malita <fmalita@gmail.com>
Signed-off-by: Adrian Bunk <bunk@stusta.de>

init/do_mounts.c

@@ -23,7 +23,6 @@ int root_mountflags = MS_RDONLY | MS_SILENT;
 char * __initdata root_device_name;
 static char __initdata saved_root_name[64];
 
-/* this is initialized in init/main.c */
 dev_t ROOT_DEV;
 
 static int __init load_ramdisk(char *str)